Surface contamination has become a major focus of research in the semiconductor manufacturing industry. The effects caused by different sources of surface contamination are responsible for most of the yield loss currently experienced. Particulate contamination has been identified as one of the prime contributors to yield loss in advanced integrated circuit (IC) fabrication.
The production process used to fabricate most integrated circuits uses chemical vapor deposition (CVD) several times, in order to produce certain layers required for proper functioning of the circuit. During CVD, different gases are burned inside a furnace, and their combustion product (a glass in vapor form) is condensed onto the surface of the wafer as well as on to other surfaces within the furnace reactor. When the process is complete and the wafers are withdrawn from the reactor, the thermal shock caused by the cooler air in the reactor furnace causes glass frost (vapox) formed on the inside surfaces of the reaction furnace to crack and become loose.
The loosened vapox particles drop onto the surfaces of the wafers subsequently processed as a source of particulate contaminants causing significant reductions in final product yield. 50 to 70% of the failures of integrated circuits are believed to be caused by contamination. Many these failures are believed to be caused from contamination by these CVD particulates. Because of this, furnaces are ideally cleaned after each critical process step and as often as possible for less critical processes.
A typical cleaning requires shutting down the furnace, removing all the gas lines, sensors, and heaters, removing the furnace liner from inside the furnace, soaking and scrubbing the liner with hydrofluoric acid, repairing the damage caused by the acid, replacing the liner in the furnace, connecting all gas lines, sensors and heaters, testing and recalibrating the furnace. A complete furnace cleaning can take from 12 to 72 hours and must be done by highly trained technical personnel. Furnaces being cleaned are not processing products, causing interruptions and disturbing the product flow throughout the facility.
While technology has focused on and advanced in the area of integrated circuit manufacturing processes there remains a need in the industry for a convenient, efficient and economical method for cleaning chemical vapor deposition reactors. Such a method would advantageously decrease the yield loss currently experienced and would be highly desirable and accepted by the industry.